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INITSTATE(3P) POSIX Programmer's ManualINITSTATE(3P)This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
initstate, random, setstate, srandom — pseudo-random number functions
#include <stdlib.h> char *initstate(unsignedseed, char *state, size_tsize); long random(void); char *setstate(char *state); void srandom(unsignedseed);
Therandom() function shall use a non-linear additive feedback random-number generator employing a default state array size of 31longintegers to return successive pseudo-random numbers in the range from 0 to 231-1. The period of this random-number generator is approximately 16 x (231-1). The size of the state array determines the period of the random-number generator. Increasing the state array size shall increase the period. With 256 bytes of state information, the period of the random- number generator shall be greater than 269. Likerand(),random() shall produce by default a sequence of numbers that can be duplicated by callingsrandom() with 1 as the seed. Thesrandom() function shall initialize the current state array using the value ofseed. Theinitstate() andsetstate() functions handle restarting and changing random-number generators. Theinitstate() function allows a state array, pointed to by thestate argument, to be initialized for future use. Thesize argument, which specifies the size in bytes of the state array, shall be used byinitstate() to decide what type of random-number generator to use; the larger the state array, the more random the numbers. Values for the amount of state information are 8, 32, 64, 128, and 256 bytes. Other values greater than 8 bytes are rounded down to the nearest one of these values. Ifinitstate() is called with 8≤size<32, thenrandom() shall use a simple linear congruential random number generator. Theseed argument specifies a starting point for the random-number sequence and provides for restarting at the same point. Theinitstate() function shall return a pointer to the previous state information array. Ifinitstate() has not been called, thenrandom() shall behave as thoughinitstate() had been called withseed=1 andsize=128. Once a state has been initialized,setstate() allows switching between state arrays. The array defined by thestate argument shall be used for further random-number generation untilinitstate() is called orsetstate() is called again. Thesetstate() function shall return a pointer to the previous state array.
Ifinitstate() is called withsize less than 8, it shall return NULL. Therandom() function shall return the generated pseudo-random number. Thesrandom() function shall not return a value. Upon successful completion,initstate() andsetstate() shall return a pointer to the previous state array; otherwise, a null pointer shall be returned.
No errors are defined.The following sections are informative.
None.
After initialization, a state array can be restarted at a different point in one of two ways: 1. Theinitstate() function can be used, with the desired seed, state array, and size of the array. 2. Thesetstate() function, with the desired state, can be used, followed bysrandom() with the desired seed. The advantage of using both of these functions is that the size of the state array does not have to be saved once it is initialized. Although some implementations ofrandom() have written messages to standard error, such implementations do not conform to POSIX.1‐2008. Issue 5 restored the historical behavior of this function. Threaded applications should useerand48(),nrand48(), orjrand48() instead ofrandom() when an independent random number sequence in multiple threads is required. These functions should be avoided whenever non-trivial requirements (including safety) have to be fulfilled.
None.
None.
drand48(3p),rand(3p) The Base Definitions volume of POSIX.1‐2017,stdlib.h(0p)
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online athttp://www.opengroup.org/unix/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017INITSTATE(3P)Pages that refer to this page:stdlib.h(0p), drand48(3p), gethostid(3p), rand(3p), random(3p), setstate(3p), srandom(3p)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |